We have an Carrier Infinity 96 furnace. When it cycles on, the blower runs at a nice, slow speed for about 5 minutes or so then it kicks into warp speed for about another 5 minutes. Why does it do that? Can I change that? The 2 guys that installed it a few years ago are long gone.

It only has a single stage t-stat. How much benefit will a two stage unit provide?

Has the blower always run as you describe, slow then warp speeds, or is this a new event. What type of thermostat do you have. Look for any documentation that may tell you about programming the control board if that's where the blower speeds are derived from.

Your climate will tell you if a 2 stage system will help. Very cold climate you may see some savings but at the expense of a more complex system to maintain. I am a believer in the Keep It Simple Stupid school of design.

The unit has operated since it was installed in the summer of '09. When the installation was complete the AC was already running. I flipped the t-stat to "heat", jacked up the set pt. and verified that the unit did operate in the "heat" mode. I saw no need to continue heating a warm house, so I went back to "cool". I didn't find out about the warp speed fan until Oct or Nov, it has always done this.

From the info in the link that you posted, the furnace relies on the motor's variable speed ability to enhance its efficiency.You're right, a 1 stage tstat ain't gonna cut it.To allow the tstat to affect blower speed in a Carrier furnace, I'll most likely need a Carrier specific tstat.I don't believe there are any compatibility rules between manufacturers that would allow brand x tstats to provide full functionality in brand y furnaces.